1. Field of the Invention
The present invention relates generally to miniature instrumentation for chemical analysis, chemical sensing and synthesis and, more specifically, to electrically controlled manipulations of fluids in micromachined channels. These manipulations can be used in a variety of applications, including the electrically controlled manipulation of fluid for capillary electrophoresis, liquid chromatography, flow injection analysis, and chemical reaction and synthesis.
2. Background of the Invention
Laboratory analysis is a cumbersome process. Acquisition of chemical and biochemical information requires expensive equipment, specialized labs and highly trained personnel. For this reason, laboratory testing is done in only a fraction of circumstances where acquisition of chemical information would be useful. A large proportion of testing in both research and clinical situations is done with crude manual methods that are characterized by high labor costs, high reagent consumption, long turnaround times, relative imprecision and poor reproducibility. The practice of techniques such as electrophoresis that are in widespread use in biology and medical laboratories have not changed significantly in thirty years.
Operations that are performed in typical laboratory processes include specimen preparation, chemical/biochemical conversions, sample fractionation, signal detection and data processing. To accomplish these tasks, liquids are often measured and dispensed with volumetric accuracy, mixed together, and subjected to one or several different physical or chemical environments that accomplish conversion or fractionation. In research, diagnostic, or development situations, these operations are carried out on a macroscopic scale using fluid volumes in the range of a few microliters to several liters at a time. Individual operations are performed in series, often using different specialized equipment and instruments for separate steps in the process. Complications, difficulty and expense are often the result of operations involving multiple laboratory processing steps.
Many workers have attempted to solve these problems by creating integrated laboratory systems. Conventional robotic devices have been adapted to perform pipetting, specimen handling, solution mixing, as well as some fractionation and detection operations. However, these devices are highly complicated, very expensive and their operation requires so much training that their use has been restricted to a relatively small number of research and development programs. More successful have been automated clinical diagnostic systems for rapidly and inexpensively performing a small number of applications such as clinical chemistry tests for blood levels of glucose, electrolytes and gases. Unfortunately due to their complexity, large size and great cost, such equipment, is limited in its application to a small number of diagnostic circumstances.
The desirability of exploiting the advantages of integrated systems in a broader context of laboratory applications has led to proposals that such systems be miniaturized. In the 1980""s, considerable research and development effort was put into an exploration of the concept of biosensors with the hope they might fill the need. Such devices make use of selective chemical systems or biomolecules that are coupled to new methods of detection such as electrochemistry and optics to transduce chemical signals to electrical ones that can be interrupted by computers and other signal processing units. Unfortunately, biosensors have been a commercial disappointment. Fewer than 20 commercialized products were available in 1993, accounting for revenues in the U.S. of less than $100 million. Most observers agree that this failure is primarily technological rather than reflecting a misinterpretation of market potential. In fact, many situations such as massive screening for new drugs, highly parallel genetic research and testing, micro-chemistry to minimize costly reagent consumption and waste generation, and bedside or doctor""s office diagnostics would greatly benefit from miniature integrated laboratory systems.
In the early 1990""s, people began to discuss the possibility of creating miniature versions of conventional technology. Andreas Manz was one of the first to articulate the idea in the scientific press. Calling them xe2x80x9cminiaturized total analysis systems,xe2x80x9d or xe2x80x9cxcexc-TAS,xe2x80x9d he predicted that it would be possible to integrate into single units microscopic versions of the various elements necessary to process chemical or biochemical samples, thereby achieving automated experimentation. Since that time, miniature components have appeared, particularly molecular separation methods and microvalves. However, attempts to combine these systems into completely integrated systems have not met with success. This is primarily because precise manipulation of tiny fluid volumes in extremely narrow channels has proven to be a difficult technological hurdle.
One prominent field susceptible to miniaturization is capillary electrophoresis. Capillary electrophoresis has become a popular technique for separating charged molecular species in solution. The technique is performed in small capillary tubes to reduce band broadening effects due to thermal convection and hence improve resolving power. The small tubes imply that minute volumes of materials, on the order of nanoliters, must be handled to inject the sample into the separation capillary tube.
Current techniques for injection include electromigration and siphoning of sample from a container into a continuous separation tube. Both of these techniques suffer from relatively poor reproducibility, and electromigration additionally suffers from electrophoretic mobility-based bias. For both sampling techniques the input end of the analysis capillary tube must be transferred from a buffer reservoir to a reservoir holding the sample. Thus, a mechanical manipulation is involved. For the siphoning injection, the sample reservoir is raised above the buffer reservoir holding the exit end of the capillary for a fixed length of time.
An electromigration injection is effected by applying an appropriately polarized electrical potential across the capillary tube for a given duration while the entrance end of the capillary is in the sample reservoir. This can lead to sampling bias because a disproportionately larger quantity of the species with higher electrophoretic mobilities migrate into the tube. The capillary is removed from the sample reservoir and replaced into the entrance buffer reservoir after the injection duration for both techniques.
A continuing need exists for methods and apparatuses which lead to improved electrophoretic resolution and improved injection stability.
The present invention provides microchip laboratory systems and methods that allow complex biochemical and chemical procedures to be conducted on a microchip under electronic control. The microchip laboratory systems comprises a material handling apparatus that transports materials through a system of interconnected, integrated channels on a microchip. The movement of the materials is precisely directed by controlling the electric fields produced in the integrated channels. The precise control of the movement of such materials enables precise mixing, separation, and reaction as needed to implement a desired biochemical or chemical procedure.
The microchip laboratory system of the present invention analyzes and/or synthesizes chemical material in a precise and reproducible manner. The system includes a body having integrated channels connected a plurality of reservoirs that store the chemical materials used in the chemical analysis or synthesis performed by the system. In one aspect, at least five of the reservoirs simultaneously have a controlled electrical potential, such that material from at least one of the reservoirs is transported through the channels toward at least one of the other reservoirs. The transportation of the material through the channels provides exposure to one or more selected chemical or physical environments, thereby resulting in the synthesis or analysis of the chemical material.
The microchip laboratory system preferably also includes one or more intersections of integrated channels connecting three or more of the reservoirs. The laboratory system controls the electric fields produced in the channels in a manner that controls which materials in the reservoirs are transported through the intersection(s). In one embodiment, the microchip laboratory system acts as a mixer or diluter that combines materials in the intersection(s) by producing an electrical potential in the intersection that is less than the electrical potential at each of the two reservoirs from which the materials to be mixed originate. Alternatively, the laboratory system can act as a dispenser that electrokinetically injects precise, controlled amounts of material through the intersection(s).
By simultaneously applying an electrical potential at each of at least five reservoirs, the microchip laboratory system can act as a complete system for performing an entire chemical analysis or synthesis. The five or more reservoirs can be configured in a manner that enables the electrokinetic separation of a sample to be analyzed (xe2x80x9cthe analytexe2x80x9d) which is then mixed with a reagent from a reagent reservoir. Alternatively, a chemical reaction of an analyte and a solvent can be performed first, and then the material resulting from the reaction can be electrokinetically separated. As such, the use of five or more reservoirs provides an integrated laboratory system that can perform virtually any chemical analysis or synthesis.
In yet another aspect of the invention, the microchip laboratory system includes a double intersection formed by channels interconnecting at least six reservoirs. The first intersection can be used to inject a precisely sized analyte plug into a separation channel toward a waste reservoir. The electrical potential at the second intersection can be selected in a manner that provides additional control over the size of the analyte plug. In addition, the electrical potentials can be controlled in a manner that transports materials from the fifth and sixth reservoirs through the second intersection toward the first intersection and toward the fourth reservoir after a selected volume of material from the first intersection is transported through the second intersection toward the fourth reservoir. Such control can be used to push the analyte plug further down the separation channel while enabling a second analyte plug to be injected through the first intersection.
In another aspect, the microchip laboratory system acts as a microchip flow control system to control the flow of material through an intersection formed by integrated channels connecting at least four reservoirs. The microchip flow control system simultaneously applies a controlled electrical potential to at least three of the reservoirs such that the volume of material transported from the first reservoir to a second reservoir through the intersection is selectively controlled solely by the movement of a material from a third reservoir through the intersection. Preferably, the material moved through the third reservoir to selectively control the material transported from the first reservoir is directed toward the same second reservoir as the material from the first reservoir. As such, the microchip flow control system acts as a valve or a gate that selectively controls the volume of material transported through the intersection. The microchip flow control system can also be configured to act as a dispenser that prevents the first material from moving through the intersection toward the second reservoir after a selected volume of the first material has passed through the intersection. Alternatively, the microchip flow control system can be configured to act as a diluter that mixes the first and second materials in the intersection in a manner that simultaneously transports the first and second materials from the intersection toward the second reservoir.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.